1. Field of the Invention
The invention relates in general to an electronic device with standby function, standby power supply system and method thereof, and more particularly to an electronic device with standby function, which can save standby power, standby power supply system and method thereof.
2. Description of the Related Art
Referring to FIG. 1A, a block diagram of a conventional electronic device with standby function is shown. An electronic device 100, a consuming electronic product such as a liquid-crystal TV, projector, or computer monitor, includes a standby power supply system 110, a relay 120 and a power load 130. The standby power supply system 110 includes a standby power transformer 112, signal sensor 114, power control unit 116 and control unit 118. Under a standby mode, the standby power transformer 112 receives an alternating-current (AC) voltage AC and transforms the voltage AC into a first direct-current (DC) voltage VCC1 and a second DC voltage VCC2. The first DC voltage VCC1 is supplied to the signal sensor 114 for maintaining its normal operation and the second DC voltage VCC2 is supplied to the power control unit 116 for maintaining its normal operation. The signal sensor 114 receives a system power-on signal S1 from a remote controller 10 and accordingly generates and outputs a control signal S2 to the power control unit 116. The power control unit 116 outputs an actuation signal S3 to the control unit 118 according to the control signal S2.
Referring to FIG. 1B, a circuit diagram of a control unit of a conventional standby power supply system is shown. The control unit 118 includes a capacitor 181 and a NPN-type bipolar junction transistor (BJT) 182. The capacitor 181 is charged by receiving the system power-on signal S3. The NPN-type BJT 182 is used as a switch. When the capacitor 181 is finished charged, the NPN-type BJT 182 is turned on and outputs a control current IC to the relay 120 for turning on the relay 120. The power supply unit 122 receives the AC voltage AC according to the turned-on relay 120, transforms the AC voltage AC into the required operational voltage VCC of the electronic device 100 and supplies the operational voltage VCC to the power load 130 as shown in FIG. 1A. However, the standby power supply system 110 has a low efficiency of power supply and consumes much standby power even under a low loading situation.